1. Field of the Invention
The invention relates to a quantum well electromagnetic wave modulator and a quantum well optical detector, more particularly applicable to the modulation or detection of several light waves.
The technical field of the invention is that of amplitude and phase modulators designed on the basis of quantum effects in semiconductors. To obtain this modulation, action is generally taken on the real and imaginary indices of a material crossed by the wave to be modulated. This action may be obtained, for example, through the application of an electrical field responsible for an electro-optical effect. In this domain of modulation, quantum semiconductor structures offer numerous possibilities, especially in the spectral ranges associated with the electron transitions that may occur either between quantum levels of different bands (namely between valence band and conduction band) or between quantum levels of the same band. In the latter case the transitions, which are then called intraband transitions, are liable to prompt very pronounced dispersal zones owing to the resonances that they bring into play. An external action that enables modification of the conditions in which these transitions occur is then capable of modifying the real and imaginary parts of the refraction indices of the materials brought into play, in the spectral range associated with these transitions. It is thus that the application of an electrical field to a semiconducting quantum well modifies the potential profile of this well and leads to a variation of the energy difference between the permitted levels that this well contains and provides a possibility of modulation. This is the Stark effect as described in R. P. G. KARUNASIRS, Y. J. MII and K. L. WANG, "Tunable Infrared Modulator And Switch Using Stark Shift In Step Quantum Wells", IEEE Electron Device Letters, vol. II, No. 5, May 90.
2. Description of the Prior Art
If the intraband transitions that cause major modifications of the optical properties of materials are to effectively occur, then the quantum levels from which they may arise should be populated (for example by electrons in the conduction and). Thus, action on this population also enables the modification of optical properties of materials. Two main options may be envisaged in order to do this. The first option consists in populating valence and conduction bands by an optical pumping operation in which the electrons are made to pass from the former to the latter. The second option uses electrical methods such as the injection of carriers.